Many kinds of produce are fragile and are subject to damage in handling and shipping. In addition, produce has a limited lifetime during which it can be sold and used. In particular, fruits such as apples and pears are easily bruised and mature rapidly after they have been picked. The invention will, accordingly, be described herein with particular reference to fruits such as apples and pears although the invention is not limited to protection and preservation of fruit and may be used as well with respect to other produce and fragile articles.
Although some fruit is sold locally by the growers, the majority of fruit and other produce is shipped a substantial distance from the field to consumers. Two problems which arise as the result of the shipping and handling of pears and apples are bruising and overripening which may result in the food becoming unmarketable or marketable only at a lesser price. In addition, even though the fruit may arrive at a supermarket or other point of sale or use in good condition, the remaining saleable life of the fruit may be so short that it passes its prime level of ripeness before it can be sold.
One method of protecting apples and pears during shipment involves the use of formed cardboard trays which include recesses that conform generally to the fruit. A tray is placed in the bottom of a standard fruit carton and is loaded with a single layer of fruit. A cushioning pad is then placed on top of this layer to protect and immobilize the fruit. This cushioning pad may comprise a layer of fibrous cushioning material in a paper envelope. Successive layers of trays, fruit and pads are positioned atop the first layer until the box is full. Although this packaging method protects the fruit against bruising it does not slow the rate of maturation of the fruit.
Although it is desirable to have unprocessed fruit available during the entire year, the fruit season is fairly short, and apples and pears ripen and begin to spoil shortly after picking if they are maintained under ambient conditions. One method of extending the life of apples and pears has been the use of controlled atmosphere storage. Fruit in good condition is taken from the fields either in boxes as described above or in bins and is placed in a refrigerated storage chamber. The temperature of such storage chamber is gradually lowered to approximately 31.degree., the oxygen level is slowly reduced to between about 1 and 5% and the carbon dioxide level maintained below 1-2%. The fruit itself aids in achieving this low oxygen level since, even at reduced temperatures, it consumes oxygen and produces carbon dioxide and water vapor.
Apples and pears can be damaged by elevated levels of carbon dioxide. For example, pears may develop a pithy brown core which results from cellular damage if the levels of carbon dioxide rises excessively. Apples may also be damaged by excessive carbon dioxide, which damage is manifested as a browning of the skin. In addition, both fruits ripen more rapidly in the presence of elevated levels of carbon dioxide. As a result, after the fruit has been loaded into a controlled atmosphere chamber, a stack of bags of hydrated lime (calcium hydroxide) are frequently positioned in the chamber of aid in maintaining the carbon dioxide level at or below the desired percentage. During storage, however, the lime in the sacks may become glazed over as the outer layers are converted from calcium hydroxide to calcium bicarbonate. This greatly reduces the rate of uptake of carbon dioxide and thus reduces the effectiveness of this method of atmosphere control. In addition, the concentration of carbon dioxide within the bins and boxes may exceed that of the ambient atmosphere to which the sacks of lime are exposed due to poor circulation within such containers. Such storage is nevertheless reasonably effective in preserving the fruit for later use. It is thus not uncommon for apples to remain in controlled atmosphere storage for several months.
Notwithstanding the benefits of controlled atmosphere storage, the fruit continues to ripen rapidly between the time it is picked and the time at which controlled atmosphere storage conditions are actually achieved. Likewise, once the fruit is removed from controlled atmosphere storage the ripening process resumes. In fact, fruit that had been stored for extended periods under controlled atmosphere storage conditions will tend to reach its peak maturity very quickly after removal from storage. As a result, such storage, while permitting the availability of fruit year round, actually shortens the effective marketable life of the fruit during which it can be transported and stored at ambient temperatures.